An air bag system such as that disclosed in JP-A-55-19627 is installed in a vehicle for protecting an occupant in a vehicle when a vehicle is involved in a collision.
Such an air bag system senses an impact at the time of a vehicle collision by an acceleration sensor. When the impact detected with the sensor is more than a predetermined value, the air bag is inflated instantly by igniting gunpowder in the air bag system by battery power. Thus, an occupant is protected. In JP-A-06-239187, even if a battery terminal is detached at the time of a collision, the air bag system can still ignite the gunpowder through a backup capacitor. Also, JP-A-06-239187 describes a system in which an engine key is used as a switch for supplying power to the air bag system. In other words, when the engine key is in an “ON” state (an engine is operating), the air bag system is supplied with power. The backup capacitor usually supplies power to the air bag system when the battery is disconnected when the engine key is in an “ON” state.
Recently, some drivers may manually turn off the engine while, for example, waiting for a long traffic light to turn green. Also, certain vehicle engine systems are designed so that the vehicle engine will turn off while, for example, a driver is waiting for a long traffic light to turn green. Both types of stops will be referred to generally as idling stops. If the driver turns off the engine during such an idling stop, the power supply to the air bag system is cut off. In other words, when the engine is “OFF,” the air bag is not actuated even if the vehicle is involved in a collision.